The present invention relates to a new process for the preparation of amines containing urethane and urea groups, to the amines obtained by this process and to their use as elasticizing hardeners for epoxide resins.
Synthetic resins based on epoxide resins are distinguished by numerous positive properties, e.g. good adherence to organic and inorganic substrates, good solvent resistance and high chemical resistance. Due to their high crosslinking density, however, epoxide resins which have been hardened with amines are brittle, with glass transition ranges above 20.degree. C. This applies particularly to those epoxide resins which are based on diphenylol propane (bisphenol A) and epichlorohydrin. These synthetic resins therefore fail to meet the practical requirements in all fields of application for which impact resistance and shock resistance as well as high flexibility are required. This applies particularly to the building industry, where permanent bridging of shrinkage cracks, e.g. in concrete, is required.
Internal increase in elasticity can be achieved to a certain extent by a reduction in the crosslink density while an external increase in elasticity may be achieved by the addition of plasticizer.
External elasticizing agents such as tar, phthalic acid esters, high boiling alcohols or vinyl polymers are not reactive and do not become incorporated in the polymer network. They only cause expansion by filling up space.
An internal increase in elasticity by reduction of the crosslink density may be achieved by reducing the functionality of the hardener. The long chain, low functional amino amides based on dimerized fatty acids which have been widely and successfully used for a long time for this purpose are, however, not suitable in all fields.
Good and permanent increase in elasticity of the epoxide resins may be obtained by a combination with polyurethanes. Thus, for example, elasticized synthetic resins of epoxide resins, polyfunctional carbamic acid aryl esters and polyamines have been described in German Offenlegungsschrift 1,252,606. Synthetic resins prepared by these means have, however, two significant disadvantages. First, the use of a three component system is not always simple. Secondly, phenols or substituted phenols are released in the course of hardening of such synthetic resins since they are not chemically bound and in the long term they migrate from the synthetic resins, with the result that the properties of the product suffer.
German Auslegeschrift 2,418,041 describes a process for the preparation of elasticized molded parts and sheet products, in which certain epoxide compounds are reacted with amine compounds which have been obtained by the hydrolysis of certain prepolymeric ketimines or enamines. Chemically resistant, firmly adhering products with improved properties may be prepared by this process. The process described, however, is relatively complicated and therefore expensive. Further, the process is not universally applicable since, as shown by our own experiments, only isocyanate prepolymers based on aliphatic polyisocyanates can be reacted with hydroxy ketimines with complete preservation of the ketimine structure.
According to German Offenlegungsschrift 2,338,256, high molecular weight, amine-terminated polyether urethane ureas are prepared by the reaction of prepolymers containing free isocyanate groups with amines in highly dilute solutions and then hardened with epoxide resins. The use of the solvents required for this process, in particular the aromatic solvents, is technically and physiologically undesirable. On the other hand, the viscosity of the solvent free reaction products is too high for practical use.
For obtaining a controlled reaction of polyisocyanate prepolymers with excess quantities of diamines, it has therefore frequently been proposed to use the polyisocyanates in a blocked form as described, for example, in Canadian Patent 1,219,986, and European Patents 293,110 and 82,983. Common to all these publications is that phenols or substituted phenols are used as preferred blocking agents. After the reaction with the polyamines, these substances either cannot be removed from the reaction mixture, or can only be incompletely removed, due to their high boiling points. If phenols or substituted phenols are left in the amine mixture or the synthetic resin mass, the disadvantages already mentioned result. These references also mention that other blocking agents conventionally used in polyurethane chemistry may also be used, such as oximes, caprolactam, malonic acid esters or acetoacetic esters.
These blocking agents, however, all have a relatively high boiling point so that they also cannot be removed or cannot be completely removed from the reaction mixture by distillation. Since none of these blocking agents can be incorporated into the polymer structure in the course of epoxide hardening, their use in place of the preferred, optionally substituted phenols provides no advantages.
The use of organic polyisocyanates blocked with secondary monoamines in combination with isocyanate reactive compounds is known from German Offenlegungsschrift 3,221,558. According to this publication, low molecular weight polyisocyanates blocked with monoamines, in particular, are combined with relatively high molecular weight organic polyhydroxyl compounds. The publication contains no information relating to the reaction of amine-blocked isocyanate prepolymers with low molecular weight polyamines.
German Offenlegungsschrift 3,311,516 relates to combinations of polyisocyanates blocked with secondary monoamines with relatively high molecular weight polyaddition, polycondensation or polymerization products containing at least two OH and/or NH groups. The specifically described reactants for the blocked isocyanates are not low molecular weight organic polyamines, but are relatively high molecular weight polyhydroxyl compounds known per se in polyurethane chemistry or relatively high molecular weight hydroxyl-containing and amino-containing compounds obtained as reaction products between low molecular weight diamines and epoxide resins.
It was an object of the present invention to provide amines containing urethane and urea groups, in particular polyamines, which would contain exclusively epoxide-reactive components and be suitable as hardeners for epoxide resins.